Description of Rummeliibacillus stabekisii gen. nov., sp. nov. and reclassification of Bacillus pycnus Nakamura et al. 2002 as Rummeliibacillus pycnus comb. nov

Abstract

Strains of aerobic, Gram-positive, rod-shaped, round-spore-forming bacteria were isolated from different geographical locations and a subsequent polyphasic study was undertaken to clarify the taxonomic position of the round-spore-forming isolates strain KSC-SF6g(T), strain M32 and strain NBRC 12622. 16S rRNA gene sequence similarities demonstrated that these strains were most closely affiliated with Bacillus pycnus NRRL NRS-1691(T) (98 %), with species of Kurthia (96 %) and Viridibacillus (94-96 %) as the next nearest relatives. However, while DNA-DNA hybridization studies showed approx. 70 % reassociation among strains KSC-SF6g(T), M32 and NBRC 12622, DNA-DNA hybridization values between these strains and B. pycnus NRRL NRS-1691(T) never exceeded 13 %. Differences in the molecular structure of the cell-wall peptidoglycan could not differentiate these strains sufficiently from other closely related genera (Viridibacillus and Kurthia). However, Lys-Asp was present in strains KSC-SF6g(T), M32 and NBRC 12622, whereas l-Lys-d-Glu was reported in B. pycnus NRRL NRS-1691(T). The menaquinone MK-7 was dominant in strains KSC-SF6g(T), M32 and NBRC 12622 and members of the genus Kurthia, whereas MK-8 was abundant in Viridibacillus species. Strains KSC-SF6g(T), M32 and NBRC 12622 exhibited fatty acid profiles consisting of major amounts of anteiso-C(15 : 0) ( approximately 50 %) and iso-C(15 : 0) ( approximately 25 %) and moderate amounts of anteiso-C(17 : 0) ( approximately 7 %), which discriminated them from closely related B. pycnus NRRL NRS-1691(T) and species of Viridibacillus (iso-C(15 : 0); 46-74 %). The authors propose that strains KSC-SF6g(T), M32 and NBRC 12622 and B. pycnus NRRL NRS-1691(T) be reclassified into a separate genus based on clear-cut differences in discriminative taxonomic markers and the distant placement of B. pycnus and the novel strains described herein from other species of this clade according to current 16S rRNA gene sequence-based relatedness ( approximately 4 % difference in sequence). We propose the placement of these isolates into the novel genus Rummeliibacillus gen. nov. For the new taxon comprising strains KSC-SF6g(T), M32 and NBRC 12622, we propose the name Rummeliibacillus stabekisii gen. nov., sp. nov. (the type species of Rummeliibacillus), represented by the type strain KSC-SF6g(T) (=NRRL B-51320(T) =NBRC 104870(T)). In addition, Bacillus pycnus, which bears traits distinct from other round-spore-forming species [i.e. absence of growth at high NaCl (7 %), positive reaction for gelatin liquefaction], is reclassified as Rummeliibacillus pycnus comb. nov. (type strain JCM 11075(T) =NRRL NRS-1691(T)) based on phylogenetic affiliations and phenotypic characterization.